1. Field of the Invention
The present invention relates generally to electro-explosive devices and activating systems therefore and, more particularly, to systems in which an explosive primer, either percussive or electric, is used to initiate an electro-explosive device.
2. Description of the Related Art
An electro-explosive device (EED), such as a bridgewire, electric igniter, electric EED, electric detonator or the like, is commonly used as a detonator to initiate an ordnance device such as a rocket, bomb, mine or other explosive charge into which the electro-explosive device has been placed. An EED, for example, typically consists of a casing containing a heat-sensitive explosive material which may be ignited by a bridgewire when the bridgewire is electrically heated by application of electrical current to the terminal wires of the EED. The bridgewire and the heat-sensitive explosive material are commonly sealed within a casing in a waterproof manner with a packing material such as plastic, the terminal wires extending through the packing material out of the EED. In a typical ordnance or explosive application, the EED is embedded into a solid rocket propellant or explosive charge, with the terminal wires from the EED leading to a battery and triggering circuit. Examples of such arrangements are U.S. Pat. Nos. 3,094,932 of Greenlees and 3,608,492 of Mitchell.
Arrangements of this type are inconvenient and inherently unreliable because they require a battery as an external source of energy. It is not feasible to incorporate batteries in products such as shells, rockets or other packaged explosives because the shelf life of such items is indeterminate. Furthermore, the connecting conductors between the energy source and the EED may fail under the shocks encountered in normal handling of the product. A variant of a system using a remote power source to fire an electric igniter is described in the Netherlands patent 7201875 which incorporates a separate unit containing a piezoelectric crystal coupled over electrical leads to the electric igniter.
Piezoelectric devices exhibit the property of converting mechanical energy to electrical energy. Impacting a piezoelectric device develops an electrical pulse between opposite faces of the piezoelectric crystal. It is known to package a piezoelectric crystal in a cartridge in association with various types of projectiles or other explosives in order that the piezoelectric device may function as a detonator for the explosive. Typical arrangements of this type are disclosed in Rotkin et al U.S. Pat. No. 2,853,012, Perkins U.S. Pat. No. 3,198,074, Calhoun et al U.S. Pat. No. 3,208,181, Vilbajo U.S. Pat. No. 3,349,709, Stresau U.S. Pat. No. 3,589,294 and Pecksen U.S. Pat. No. 3,859,746. Also see French patent 2,400,688.
In order to minimize the external mechanical force needed to energize the piezoelectric crystal, it is known to incorporate an explosive primer with the piezoelectric element so that activation of the primer results in an explosion which is directed to the piezoelectric crystal, thereby multiplying the mechanical energy initiated by the firing pin to the mechanical pulse that impinges on the piezoelectric crystal. Such an energy converting device is the subject of U.S. Pat. No. 2,970,545 of Howe.
A similar arrangement is disclosed in United States Statutory Invention Registration No. H210 of Harris wherein the explosive primer is ignitable by a bridgewire. Harris requires the application of a high voltage signal simultaneously for safety purposes.
U.S. Pat. No. 5,040,463 of Beaverson discloses the use of a high pressure gas to actuate a firing mechanism by firing a detonator which shocks the piezoelectric element to develop the firing pulse for the associated main explosive.
U.S. Pat. No. 3,859,746 of Pecksen discloses a spring-biased impacting element which, upon release, drives a piezoelectric voltage generator to develop the electrical pulse needed to ignite the detonator of an associated propellant charge. A similar arrangement is disclosed in U.S. Pat. No. 2,827,851 of Ferrara. A plethora of similar references indicates that piezoelectric devices in association with an electrically energized detonator are well-known in the art and that some of these arrangements may incorporate a primary percussive element to develop the mechanical force required for activating the piezoelectric element.